function plus(){
        var num1 = document.getElementById("num1").value;
        var num2 = document.getElementById("num2").value;
        var result = parseInt(num1)+parseInt(num2);
        document.getElementById("result").value=result; 
    }
    function jianfa(){
        var num1 = document.getElementById("num1").value;
        var num2 = document.getElementById("num2").value;
        var result = parseInt(num1)-parseInt(num2);
        document.getElementById("result").value=result; 
    }
    function chengfa(){
        var num1 = document.getElementById("num1").value;
        var num2 = document.getElementById("num2").value;
        var result = parseInt(num1)*parseInt(num2);
        document.getElementById("result").value=result; 
    }
    function chufa(){
        var num1 = document.getElementById("num1").value;
        var num2 = document.getElementById("num2").value;
        var result = parseInt(num1)/parseInt(num2);
        document.getElementById("result").value=result; 
    }